FAQ's about antibiotics in animal feed

In a Dec. 22 notice, the FDA announced it will no longer pursue the withdrawal of the antibiotics penicillin and tetracycline from use in animal feed. Some worry that without the withdrawal of these antibiotics, there could be rise in antibiotic-resistant bacteria. To better understand the FDA decision, it could help to review the basics of antibiotic use in animals.

This pig's ears are infected with a strain of Staphylococcus bacteria. Many producers give their animals antibiotics to prevent such infections. Image courtesy of the National Agricultural Library.

Why do livestock producers use antibiotics?

Antibiotics are useful for controlling and preventing disease in livestock. Proper use can keep animals healthy, control the spread of diseases between herds, help animals gain weight, and prevent the spread of diseases from animals to humans.

Why are some antibiotics called “growth promotants?”

In the U.S., many livestock producers give their animals low doses of certain antibiotics to improve overall health and help animals gain weight. This is also called “subtherapeutic” use because instead of curing a specific disease, the antibiotics are used to improve overall growth and health.

Since the 1940’s, scientific studies have shown that antibiotics may improve animal growth by improving gut health. Animals play host to many kinds of gut microbes. Though many gut microbes aid in digestion and immune response, they also compete with animals for nutrients. A 1994 study showed that as much as 6% of the net energy in the pig diet is lost to organisms in the gut. Antibiotics in animal feed can reduce this competition and help an animal gain weight more efficiently. Low doses of antibiotics can also ward off “subclinical infections” that stress the animal’s immune system and slow growth.

Use of growth-promoting antibiotics is one way livestock producers meet global demand for food. In 2002, Dr. Gary Cromwell, a professor of swine nutrition at the University of Kentucky, published a paper showing that antibiotics dramatically improved pig growth. Cromwell analyzed the results of more than 1,000 growth experiments in swine over a 25-year period. In young pigs, antibiotics improved the growth rate by an average of 16.4%.

Are antibiotics safe in animal feed?

In the Dec. 22 notice, the FDA reported that after 34 years of hearings on the issue, there is still no direct link between antibiotics in animals and drug-resistant human diseases. The FDA has recommended further studies on the issue.

Despite the lack of direct evidence, several organizations have spoken out against the FDA decision. Many animal scientists blame this opposition on common misconceptions about antibiotic use.According to the American Meat Science Association and the American Meat Institute, “One often-cited statistic comes from the Union of Concerned Scientists, which claims that 70 percent of antibiotics produced in the U.S. are fed to livestock, a statistic they cannot possibly calculate considering that antibiotic use in humans is not tracked.

“Even so, one would expect the 302 million head of American livestock and 6.27 billion American chickens and turkeys to require more antibiotics than 309 million people who weigh a fraction of a full grown steer and far less than a typical market hog.”

Though there is not a direct link between antibiotic use in animals and antibiotic-resistant bacteria in humans, it is important to remember that antibiotic use — whether in human or animal medicine — could lead to resistant bacteria. In its recent announcement, the FDA emphasized the need for continued research.

“FDA continues to view antimicrobial resistance as a significant public health issue,” wrote the administration.

As scientists study this issue, livestock producers can also take steps to keep their herds healthy. According to Jeannine Schweihofer, District Extension Educator for beef and livestock at the Michigan State University Extension, responsible livestock producers follow very specific guidelines for antibiotics use.

“Several industry groups, including the American Veterinary Medical Association, American Association of Bovine Practitioners, National Cattlemen’s Beef Association, National Pork Board, Poultry Science Association, and more support judicious use of antimicrobials and have recommendations in place to ensure the proper use of these drugs,” Schweihofer writes. “Some of these judicious use principles include:

-Use of antibiotics should be under the direction of a licensed veterinarian
-Only using antibiotics according to the label; they should be used to prevent or control disease
-A veterinarian-client-patient relationship is required for extra-label use of antimicrobials
-Preventative strategies including proper care and management of animals, regular health monitoring, and use of vaccinations to prevent disease are important
-Avoid using antibiotics that are important in human medicine
-Treat the fewest number of animals possible
-Use as narrow of a spectrum of antimicrobials as possible
-Strictly adhering to withdrawal times
-Keep records of use of antimicrobials
-Properly handle and dispose of all animal health products, including antibiotics to protect the environment”